Controlling the Water Absorbency of Agricultural Biopolymers

Natural biodegradable polymers made from agricultural products, such as soy protein isolateand corn starch, have poorer water resistance than synthetic polymer derivedfrom petrochemicals and thus absorb more moisture. As a result, commercial exploitation of agriculturally derived materials has been very limited. The targeted applications for the natural biodegradable polymers require that the materials have sufficient stiffness and strength during their useful life, but eventually biodegrade. Achieving this required combination of properties from the biodegradable polymers is very difficult because of their inherent water sensitivity and relatively low stiffness and strength, especially in moist environments.

To address these problems, the author recently initiated a long-range research project todevelop affordable, stiff, strong bioabsorbable polyphosphate filler/soy-protein polymer composites, along with methods for making practical shapes from these products. The research involves blending special bioadsorbable polyphosphate reinforcing filler shaving low glass transition temperature and the biodegradable soy-protein polymer using a single-screw (or twin-screw) extruder at temperatures above thepolymer's melting point. The blendedsoy-protein polymer composite containing the required amount of the reinforcing fillers is then either injection molded of compression molded in to articles of various shapes and sizes.

Blending the bioadsorbable polyphosphate reinforcing fillers and biodegradable soy-protein polymer enables the production of stiff, strong bioadsorbable filler/polymer composites with properties superior to those of pure soy-protein polymers. Both the filler and the polymer are nontoxic and bioadsorbable, making them excellent choices for such applications as medical/surgical devices and food packaging, and for other disposable food products that must safely biodegrade after their useful service life. The chemical nature of the filler (i.e.,polyphosphates) and soy proteins [i.e., poly(amino acids)] indicates that recycled products made from these materials can be used as soil conditioner sand/or animal nutrients, eliminating most of the problems of recycling orreusing synthetic polymer made from petroleum-based precursors.